The present invention relates to a method for increasing the brightness retention of washed fabrics, where use of commercial laundry detergents in the washing liquor introduces a desirable amount of optical brightener thereto, and the use of hypochlorite bleaches ordinarily reduces the retained brightness, but the special formulation of the bleaches herein surprisingly mitigates the brightness-reducing action of said hypochlorite bleaches. Since it is desirable to use hypochlorite bleaches for their effective cleaning, oxidizing, deodorizing and sanitizing capabilities, the inventive method emphasizes an added advantage thereof.
Thickened hypochlorite bleach solutions or compositions have long been used in a variety of applications including hard surface cleaning, disinfecting and the like. These compositions are typically provided with increased viscosity for a number of reasons, principally to increase residence time of the composition on non-horizontal surfaces. However, these compositions have not been used in the laundering of fabrics, typically, because their formulation as thickened cleaners emphasizes their use on surfaces or in drain care products, where the need to adhere to such non-horizontal surfaces, as well as the use of strong alkalis teaches away from use as a laundry additive.
Some references describe the unique phenomena that occurs when certain charge-bearing surfactants, such as quaternary ammonium compounds or betaines, are combined with a source of a counterion. U.S. Pat. Nos. 4,900,467, 5,011,538 and 5,055,219, all issued to Smith (and of common assignment herein), provide exemplary cleaning compositions generally characterized as viscoelastic.
Hynam et al., U.S. Pat. No. 3,684,722, teach that a combination of an amine oxide surfactant (which is referred to in Hynam as a xe2x80x9chydrotropexe2x80x9d) and a fatty acid soap will impart desirable thickening attributes to, apparently, a surface cleaner. Although Hynam recognizes that hypochlorites are used in laundry applications, its principal objective is to form a cleaner which can adhere to a vertical surface. (See column 1, lines 55-58; and column 3, lines 43-50). On the other hand, Hunting, U.S. Pat. No. 3,560,389, teaches the use of an amine oxide surfactant combined with what is commonly defined as a hydrotrope, such as sodium xylene sulfonate, but for the purpose of chemically stabilizing the resulting all-in-one xe2x80x9cdetergent bleach.xe2x80x9d Because of the requirement in laundry for oxidant-sensitive additives such as enzymes and fluorescent whitening agents, which exhibit instability in the presence of hypochlorite, it is anticipated that the inventive formula would be used in conjunction with a commercially available laundry detergent rather than be used as an all-in-one product. Neither Hynam nor Hunting teach, disclose or suggest that hypochlorite bleaches formulated with effective amounts of bleach stable nitrogen-atom-bearing surfactants and either a bleach stable anionic surfactant or a hydrotrope will surprisingly enhance the brightness retention of fabrics washed therewith in conjunction with a separate, commercial laundry detergent. Further, Colbom et al., U.S. Pat. No. 4,863,633, describes a non-thickened hypochlorite bleach specially formulated with very little (no greater than 100 ppm) surfactant in order to mitigate stress-cracking in thin-walled thermoplastic bottles housing such hypochlorite bleach, such bottles being subject to load-sharing when stacked in corrugated cartons containing such bottles.
In one aspect of the invention, the invention provides a method for increasing the brightness retention of a laundered fabric after numerous washing cycles, said method comprising:
a) adding to an aqueous wash liquor a quantity of a commercial laundry detergent which delivers at least 0.1 g of an optical brightener into said wash liquor;
b) adding prior to, concurrent with, or after step a) a bleaching composition in an amount of at least about 0.5 g/L, wherein said bleaching composition comprises
(i) about 2.5-10% alkali metal hypochlorite;
(ii) about 0.05-5% bleach stable surfactant bearing at least one nitrogen atom;
(iii) a bleach stable anionic surfactant or a hydrotrope, wherein the ratio of (ii) to (iii) is between about 10:1 to about 1:10; and
(iv) an effective amount of a source of alkalinity;
c) adding prior to, concurrent with, or after steps a) and/or b) at least one fabric work;
d) contacting said fabric work with said wash liquor repeatedly in one washing cycle; and
e) repeating steps a) through d) at least five times;
wherein the optical brightener deposited on said fabric work increases versus a control in Stensby whiteness measure of at least about xcex94W=4.
It is an object of this invention to improve the brightness retention of fabric works washed in aqueous wash liquors with standard commercial detergents and a specially formulated hypochlorite bleach composition.
It is another object of this invention to provide a hypochlorite bleach with relatively small amounts of surfactants and hydrotropes/anionic surfactants which are nonetheless effective to mitigate the oxidation, destruction or deactivation of optical brighteners contained in commercial laundry detergents used to launder fabrics.
It is yet another object of this invention to improve the appearance of fabrics laundered multiple times, through the enhanced retention of brightness.
It is also an object of this invention to improve the performance one achieves by laundering fabrics with commercial laundry detergents and the specially formulated hypochlorite bleach.